Migrant health has increasingly attracted attention in the contemporary global health policy dialogue. The World Health Organisation (WHO) first acknowledged the issue at the 61st World Health Assembly in 2008, encouraging WHO members to ensure the right to health for migrants. The matter is also mentioned in the 2030 Sustainable Development Goals, which argued that a mechanism for achieving these goals is to offer health insurance and health services for all migrants. Thailand is one of many countries where the issue of migrant health is on the national agenda because of the country’s reliance on migrant labour. This research aims to understand how the issue of migrant health insurance and services is constituted as a ‘problem’ in the 2013 Migrant Health Insurance Card Scheme policy and its practices. This policy is targeted at undocumented migrants who face challenges when accessing health services and registering for health insurance. This study uses a poststructural discourse analytic strategy guided by Bacchi’s (2009) What’s the problem represented to be? approach and Bacchi and Bonham’s (2016) Poststructural Interview Analysis approach to explore the 2013 Migrant Health Insurance Care Scheme. It uses policy document analysis and in-depth interviews with policy agents to analyse the discourse in policy problematisation practices. Moreover, it compares the problematisation process in two border provinces (one at the Myanmar border and the other at the Laos PDR border) to reveal the different discourses of health security, neoliberal health and human rights that shape the issue and highlight the effects on health policy stakeholders’ practices. These discourses and discourse attributes like Thai bureaucratic culture reveal the power/knowledge relationship in legitimising the different migrant health understandings between institutions and locations. This thesis introduces the use of critical policy analysis to the Thai public health research community, offering an alternative analytical approach for health policy based on discourse sensitivity. It provides opportunities for rethinking the policy problem and establishing an analytical health policy approach based on discourse sensitivity in ways that can mitigate unintended harmful consequences for migrants and improve migrant health services.